Pitch control mechanism



DCC. 31, 1946. G, F, BRAKE FITCH CONTROL MECHANISM Filed Sept. l5, 1941N EaNTOg-J l Geo/ye Sgr/@5f ,0f e

Patented Dec. 31, 1946 PITCH CONTROL MECHANISM George Forrest Drake,Rocl'rford, Ill.; assigner to Woodward Governor Company, Rockford, Ill.,a corporation of Illinois Application September 15, 1941, Serial N o.410,807

6 Claims.

This invention relates to mechanisms for controlling the pitch ofpropcllers for aircraft or the like and has more particular reference tomecham'sms of the hydraulic type.

The general object is to equip a propeller adjusting mechanism of theabove character with selectively operable means by which the propellerblades may be locked positively at some fixed pitch so as to assist inproper setting of the carburetor mixture of the engine by which thepropeller is driven.

Another object is to provide such a blade lock in which the pitchadjusting servo is utilized to apply the locking force.

A further object is to provide an hydraulic blade lock which is notaffected by leakage of pressure fluid at the rings through which the uidis transferred from the stationary to the rotating parts.

Still another object is to adapt the blade locking mechanism for controlfrom a remote point.

It is another object to utilize the auxiliary feathering pump as asource of locking pressure.

The invention also resides in the novel arrangement of valves by whichthe locking action is effected.

Other objects and advantages of the invention Will become apparent fromthe following detailed description taken in connection with theaccompanying drawing which is a schematic view and circuit diagram of anhydraulic pitch control mechanism involving the novel features of thepresent invention.

.The invention is susceptible of various modiications and alternativeconstructions and of use with various kinds of blade adjusters, and Ihave shown in the drawing and will herein describe in detail a preferredembodiment of the invention applied to a common type hydraulic adjustingmechanism. It is to be understood, however, that I do not intend tolimit the invention by such'disclosure but aim to cover al1modifications and alternative constructions and uses falling y the nowof oil is metered by a valve 9 actuated l in response to engine speedchanges detected by a centrifugal 'governor I0. As shown, the governorincludes a rotary head II pivotally supporting yballs I2 having armsbearing upwardly against the head I3 of a valve rod I4 which is urgeddownwardly by an adjustable Speeder spring I5. The ball head II is onthe upper end of a sleeve I6 journaled in the governor casing and drivenfrom its lower end through a gear connection I1 with the enginecrankshaft 2. The

valve rod has a land I8 which cooperateswith a port I9 in the sleeve I6,the latter in turn communicating with a conduit 20 constituting theoutlet of a booster pump 2l. Oil is delivered to the pump from a branch22 leading from the outlet of a gear pump 23 that supplies oil at lowpressure to the engine lubricating system. The pressures developed bythe pumps are determined by the setting of by-pass valves 24 and 25,

The lower end of the valve sleeve I6 may be opened and closed accordingto the positionv of a land 26 on the lower end of the stem I4.Intermediate the lands IB and 26, the sleeve is ported and communicateswith a conduit 2l which leads through valves 28 and 29 and the usualtransfer ring 30 to a valve 3| which forms a part of the present bladelock control and the usual distributor valve 32, both valves beingdisposed within the engine shaft 2. The distributor valve comprises aplunger 33 slidable in a cylinder 34 and having spaced lands 35, 3B, 3'Iand 38. The cylinder communicates through ports 39, 40 and 4I with asupply conduit 6I leading from the transfer ring 30. A conduit 42extends from a port 43 to the head end of the cylinder 6 while the rodduit 44 with a port 45 between the lands 3'I and peller is driven. Theblades are mounted on the end of the engine crankshaft 2 which projectsforwardly through a hub 3 at the front of the engine frame 4. The bladepitch is changed by an hydraulic actuator or servo rotatable with the38. Another port 46 opening between the lands 36 andv 3'I leads througha conduit 4l to a collector ring 48 which is connected through a conduit49 and a valve 58 to the supply line of the lubricating pump 23. Apressure relief valve 5I is connected to the line 49 and set to pass oilat a pressure somewhat above that delivered by the position shown inwhich the land 35 abuts against a shoulder 54.

'Ihe plunger 3I of the valve 3| is slidable in a cylinder 52 throughwhich the supply conduitBI extends. A spring 55 strong enough toovercome the normal pressure of the lubricating system urges the plungerto the left as shown, a piston 56 then being disposed in the remote endof the cylinder which communicates through a. port 51 with the conduit41.

The valve 29 has a rotary member 58 through which extends a passage 59which, when turned to the position shown in dotted outline, interruptsthe ow of pressure fluid through the conduit 21 to the distributor valve32. An arm 60 fast on the Valve member is connected to a rod 62 whichcarries the armature of a solenoid 63 energizable by closure of a switch64 at a remote point of control. When the solenoid is deenergized, a

spring 14 holds the Valve 29 in open position as the casing 65 of thevalve 56 communicates with a. conduit 66 leading to a, cylinder 61 inwhich there is the piston 68 of the Valve 28. This is normally urged bya spring 69 to the position shown in which fluid is permitted to flowthrough the conduit 21. Opposite the conduit 22, the valve casing 65communicates with a conduit y1IIa leading'to the outlet of a gear pump'1driven by an electric motor 1I and having its inlet 12 connected to theoil supply line 22. This pump is adapted to provide fluid pressure forfeathering the propeller. The circuit for the motor 1| is closed underthe control of a switch 'I3 in the control cabin.

The valve 50 has a, member 16 rotatable within the casing 65 andcarrying an arm 11 connected to the rod 62 for actuation of the twovalves in unison under the control of the solenoid 63. In the normalposition shown, the member 16 is positioned to connect the conduits 22and 49 and also the conduits 66 and 10e. In the other position of themember shown in dotted outline, the conduits 49 and 1|]a are connectedand 66 is connected to the conduit 22.

The circuit arrangement thus far described is that of the so-calledhydromatic control with the addition of the valves 29, 3| and 50. partswill be positioned as 'shown when the engine is operating at the speedcorresponding to the setting of governor speeder spring I5. An increasein engine speed raises the pilot valve member I4 admitting oil from thegovernor pump into the sleeve I6. The oil ows through the cut-off valve28, the transfer ring 30, valve 3l, passage 6I, ports 39 and 45 of thedistributor valve into the rod end of the cylinder 6. When the pressurethus applied to piston 5 exceeds the com- -bined forces urging theblades toward low pitch, the piston moves outwardly, and oil in the headend of the cylinder is displaced into the engine lubricating system. Itspath is through tube 42 distributor valve ports 43 and 46, conduit 41,transfer ring 48, Valve 56, and pump relief valve 25. The outward motionof the piston 5 is translated into rotary motion of the cam 1 which,through bevel gears increases the blade angle. This increase isaccompanied by a decrease in engine speed and, because ofdecreasedrcentrifugal force, the governor yweights move inwardly Thegovernor pump is discharged through the relief valve 24.

When the engine speed drops below the Set Value, the flyweights moveinwardly, lowering the pilot valve and allowing oil from the rod end ofthe cylinder to flow back through the distributor valve into thegovernor, where it is discharged through a governor drain port which isthen opened by the land 26. Under the action of centrifugal twistingmovement and engine oil pressure, the blades now assume a lower angle,the engine speed increases, and the pilot valve rises due to the outwardmotion of the ilyweights. When the engine has reached the speed forwhich the governor is set, the pilot valve again assumes a neutralposition, neither admitting oil`to nor draining it from the propellercylinder. The forces are then in equilibrium and again the propellerruns at the selected speed.

To feather the propeller, it is only necessary to start the motor 1I byclosing its control switch 13. The pump 10 supplies oil at a pressuresubstantially higher than the governor pump causing the piston 68 tomove and close the valve 28 thereby disconnecting the governor.taneously, the valve connects the high pressure oil conduit 66 to theconduit 21, permitting oil to flow to the rod end of the cylinder 6 asdescribed above, causing the piston 5 and the cam rollers 1a to moveunder the increased pressure to the feathering or lowmechanical'advantage portion of the cam 1. Then the pressure builds uprapidly and this increase may be utilized to actuate means (not shown)for deenergizing the motor 1I, :the blades remaining feathered. Duringfeathering, the position of the distributor valve is not changed, thepressure being insufficient to overcome the spring 53 which acts on theplunger 33.

To unfeather, the switch 13 is held closed and the pressure cut-outswitch above referred to is prevented from operating. High pressure oilis again delivered to the rod end of the cylinder. As the pressure inthe distributor valve increases, the plunger 33 moves against the spring53 and above the feathering pressure the land 31 covers the port 45disconnecting the supply line from the rod end of the cylinder 6. 4- Asthe pressure rises to a predetermined higher value, the land 31 passesthe port 45 thereby connecting the head end of the cylinder to thesupply line 6| through ports 4I and 43, the rod end being connected tothe low pressure line 41 through ports 45 and 46. Under this increasedpressure, the piston 5 moves inwardly unfeathering the blades andforcing oil from the rod end of the cylinder into the lubricatingsystem. Then, the blades begin to windmill. When a predetermined speedis attained, the control switch 13 is released, stopping the motor 1Iand allowing the distributor and cut-off valves to return to theirnormal positions so as to transfer the control of the pitch actuatorback to the governor.

To lock the blades in xed position as during adjustment of the enginecarburetor, it is only necessary to close the switches 64 and 13 withSimula the rod 62 and changes the positions of the valves 29 and 50, theformer disconnecting the governor from the `regular supply line 21. Thevalve 50 not only disconnects the pumps 23 and 10 from the propellerservo through the normal supply lines, but also connects the outlet 1liaof the feathering pump 10 to the conduit 49. With the parts thuspositioned, oil from the pump 10 is delivered at a pressure determinedby the setting of the relief valve 5I and somewhat higher than thelubricating oil pressure. The oil flows through the conduit 49I and thetransfer ring- 48 into the passage 41 and, since `the line 6I is thenclosed by the valve 29, the pressure in the passage 41 risessufficiently to move the piston 56, the valve plunger 3|a thus beingshifted against the action of the spring 55 to close the conduit 6|against the escape of oil from the distributor valve 32.

The oil pressure thus created by the pump 10 is applied to the head endof" the servo piston through the conduit 41, ports 46, 43 of thedistributor valve, and the conduit 42, this pressure supplementing thecentrifugal moment tending to turn the blades toward low pitch. Suchmovement of the piston is prevented, however, because the passageleading to the rod end of the cylinder 6 through the distributor valveports 45, 39 is blocked off or closed by the valve 3l. It will beobserved that the point of closure is in the rotating parts and betweenthe distributor valve 432 and the transfer ring 30 so that there is noleakage from the cylinder 6. That is, oil is trapped effectively in therod end of the cylinder and that portion of the conduits and dis'-tributor valve between the valve 3| and the cylinder. The oil, beingnon-compressible, provides in effect a positive stop preventing movementof the piston 5 toward the rod end of the cylinder thereby locking thepropeller blades against movement toward low pitch. The combinedcentrifugal moment and the oil pressure acting on the piston 5effectively holds the blades in the locked position during rotation ofthe propeller.

After the engine adjustments have been made, the switches 64 and 13 areopened. This stops the pump 10 and allows the valves 29 and 50 to bereturned by the spring 14 to their normal po-v sitions restoring theregular governor control.

From the foregoing, it will be seen that the servo that normally adjuststhe blades to maintain a constant engine speed is utilized to produce,the force for locking the propeller blades in their limit positions.One of the fluid conduits leading to the servo is utilized to producethe hydraulic stop by which the limit position of the blades isdetermined. This stop is adjustable simply by running the engine at aspeed corresponding to the fixed pitch desired preparatory to operatingthe valves 29 and 50 to disable the governor control and lock the bladesat a xed pitch. By using the valve 3| to trap oil in the rod end of thecylinder 6, the centrifugal force component acting on the blades assistsin holding the latter in the locked position. This permits a low oilpressure to be employed for locking purposes.

I claim as my invention:

1. The combinlahti'en ofan engine having a low pressure lubricatings`y`s`teiillrand.laE propeller driven by said engine and having bladestending to turn toward low pitch when the propeller is rotating, meansincluding a piston movable in opposite directions to increase anddecrease the pitch of said blades, a cylinder for said piston rotatablewith said propeller, a rst iiuid con-k duit including a transfer ringbetweenf the rotating and non-rotating parts and connecting saidlubricating system to one end of said cylinder wherebir the low pressurefluid urges said blades toward low pitch, means providing a of fluidfrom said second source tosaid second conduit, means providing a thirdsource of pressure fluid, higher than said lubricating pressure and saidsecond source of pressure, e normally open valve in said second conduitbetweensaid cylinder and said second transfer ring and adapted to closeautomatically in response to a fluid pressure in said first conduithigher than said lubricating pressure, and valve means in thenon-rotatable portions of saidV conduits selectively operable to connectsaid lubricating and second pressure sources to said rst and secondconduits respectively in one position of the valve means to close saidsecond conduit and connect said third pressure source to said rstconduit inthe other position of the valve means.

"2. The combination of an hydraulic servo for adjusting the pitch ofpropeller blades including a double acting piston and cylinder, meansfor supplying fluid under pressure to one end of said cylinder, valvemeans operable in a plurality of different positions of said blades, andmeans dependently of the blade positions to trap fluid in the othercylinder end and thereby lock the propeller blades at a fixed pitch.

3. The combination of a servo for adjusting the pitch of power drivenpropeller blades, means responsive to the speed of the propeller tocontrol said servo and adjust said blades for the maintenance of apredetermined propeller speed, a normally inactive stop adapted whenactive to limit the adjustment of said blades by said servo, manuallycontrollable means selectively operable to render said stop active inany one of a plurality of different positions of said blades, and meansoperable automatically as an incident to rendering said stop active toenergize said servo independently of said speed responsive means andhold the blades against said stop.

4. The combination of an adjustable pitch propeller, an hydraulic servorotatable with said propeller for actuating the same, means forsupplying pressure fluid to said servo including fluid conduits leadingthrough transfer rings to and from opposite ends of Ithe servo, apressure actuated valve disposed in one of said conduits between thetransfer ring thereof and said servo and selectively operable in aplurality of different pitch settings of said propeller to open andclose the conduit whereby to trap iiuid in one end of said servo whenthe valve is closed and thereby the propeller against the stop formed bysaid trapped fluid.

5. AThe combination with a hydraulic servo for adjusting the pitch ofpowei` driven propeller blades, means providing a source of uid underpressure, means responsive to the rotational speed of the propellerblades and controlling the ow of said fluid to and from said source, anormally inactive stop adapted when rendered active to limit theadjustment of said blades by said servo, means providing a source offluid under a pressure higher than said first mentioned pressure, andmanually controllable means selectively operable to render said stopactive at any selected one of a plurality of different positions of saidblades to render said stop active and admit uid from said second sourceto said servo to energize the latter and hold the blades against saidstop.

6. The combination with a hydraulic servo for adjusting the pitch ofpower driven propeller blades, means providing a source of fluid underpressure, means responsive to the rotational 'speed of the propellerblades and controlling the ow of said fluid to and from said source, anormally inactive stop adapted when rendered active to limit theadjustment of said blades by said servo, means providing a source ofiiuid under a pressure higher than said rst mentioned pressure, valvemeans responsive to the pressure of uid from said source to render saidstop effective, and manually controllable means selectively operable atany one of a plurality of different positions of said blades to disablesaid speed responsive means and energize said valve means from saidsecond source.

GEORGE FORREST DRAKE.

